1. Field of the Invention
The present invention relates to a method for time synchronization of a computer network, preferably of a switching computer system, including at least one main computer (Master) with, in each case, at least one assigned secondary computer (slave), each computer being provided with at least one internal clock, and the computers being connected via at least one ATM bus (ATM=asynchronous transfer mode).
Furthermore, the present invention relates to a computer network, preferably a switching computer system, including at least one main computer (Master) with, in each case, at least one assigned secondary computer (Slave), each computer being provided with at least one internal clock, and the computers being interconnected via at least one ATM bus.
2. Description of the Prior Art
At present there is no known prior art for real-time process computer systems, particularly switching computer systems, in which time synchronization of the participating computers in the computer network is achieved with an accuracy with regard to date and time of day of at least +/−50 msec and a relative time stamp of at least +/−1 msec. The currently used switching computer systems such as, for example, the applicant's switching computer system EWSD or EWSX, are achieved either as mono-processor systems or strictly coupled multi-processor systems. With this type of configuration, particular time synchronization is inherently given on account of the strict coupling of the processors, or of the just one processor that is present.
In the course of general development, however, distributed real-time process computer systems are also intended to be used as switching computer systems. The requirement for charge registration necessitates the process computers situated in the process computer system to be provided with a synchronized time, with regard to date and time of day, which has a maximum error of +/−50 msec. This requirement is substantiated by the charge registration since the charge registration creates tickets with a time indication at all the computer components of the distributed system. Furthermore, it is necessary, on account of the internal data transport protocol of the distributed system, to achieve a relative time stamp, or a counter, with an accuracy of at least +/−1 msec for all the computers in the network system. The relative resolution of such a time stamp, that is to say the time spacing from one counter to the next counter, typically lies in a range of about 10 msec. The time stamp is required in order to measure message throughput times in the system, so as to analyze incorrect behavior or to carry out performance analyses in the distributed system, with the aid of system tracers. In order for the events from the trace results to be correctly assigned with respect to time, a system-wide synchronized time of day, that is to say a correspondingly exact time stamp, is likewise required.
It is an object of the present invention, therefore, to present a method for time synchronization of a computer network, preferably of a switching computer system, and a corresponding computer network, preferably a corresponding switching computer system, which achieves time synchronization for date/time of day of at least +/−50 msec and for a general relative time stamp of at least +/−1 msec, using no direct connection between the individual computers, but rather only the ATM bus.